End of travel indicator variable resistance device



Feb. 11, 1969 L, 1-. PEART ETAL END OF TRAVEL INDICATOR VARIABLE RESISTANCE DEVICE Sheet of 2 :"ilai Nov. 1, 1967 FIG. 4

Fee. 2

Has

w m m m INVEN'TORfi; LESLIE T PEART V CHAR ES w. YUNGBLUT BY ATTOR Y Feb. 11, 1969 L, PEART ETAL 3,427,546

END OF TRAVEL INDICATQR VARIABLE RESISTANCE DEVICE M *0? l, 1967 Sheet 2 of? INVENTORE LESLIE T PEART CHAR ES W. YUNG BLUT BY W ATTORN United States Patent 3,427,546 END OF TRAVEL INDICATOR VARIABLE RESISTANCE DEVICE Leslie T. Peart, Santa Ana, and Charles W. Yungblut, San Diego, Calif., assignors to Beckman Instruments, Inc., a corporation of California Filed Nov. 1, 1967, Ser. No. 679,919 U.S. Cl. 338180 Int. Cl. H01c /02 2 Claims ABSTRACT OF THE DISCLOSURE This invention is particularly applicable to a rectilinear type variable resistance device commonly known as trimming potentiometers which employ a threaded shaft for moving a contact member over a resistance element between predetermined positions.

Potentiometers of the trimmer class function mainly as auxiliary resistance adjusting devices and, many of such devices employ a threaded screw member which is rotated to adjust the position of a movable electrical contact adapted to traverse a resistance element mounted within a suitable housing. When the contact is moved to the end of its path adjacent the ends of the resistance element, it is restrained from further movement by stop means formed within the housing. The contact carrier is usually carried on a nonconductive block which is provided with a clutch mechanism which permits the threaded shaft to disengage from the contact carrier block when further movement thereof is restricted by the stop means. While some presently available clutch mechanisms produce a signal, such as an audible signal or a difference in feel in the applied rotational force, it is impossible, in many such devices, for the operator to detect when the contact is at the end of its travel. In such cases an operator must rely on a meter or other such means, for this information.

Accordingly, it is an object of the present invention to provide a new and improved mechanism for drive screw actuated variable devices which produces an audible signal to signify when the contact has reached its respective limits of travel.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings in which:

FIGURE 1 is a perspective view of a rectilinear trimmer of the type in which the invention is particularly applicable;

FIGURE 2 is an enlarged plan view of a portion of the trimmer illustrating the drive screw and the contact carrier mechanism;

FIGURE 3 is an enlarged side view of one embodiment of the clicking member;

FIGURE 4 is a view taken from the bottom of the clicking mechanism of FIGURE 3;

FIGURE 5 is an end view of the apparatus taken substantially along line 55 of FIGURE 2;

FIGURE 6 is an enlarged perspective view of another embodiment of the clicking mechanism;

FIGURE 7 is an enlarged plan view of a portion of a trimmer illustrating the attachment of the clicking mechanism of FIGURE 6; and

FIGURE 8 is an enlarged elevation view of the contact carrier and the clicking mechanism of FIGURE 7 taken substantially along line 88.

Referring now to FIGURE 1, the reference numeral 5 refers to a rectilinear trimmer potentiometer including a housing, formed in a rectangular shape. As shown in FIG- URE 2, the housing includes a plurality of side walls and end walls enclosing a recess 9 in which are mounted the function-a1 components of the potentiometer. The end wall 8 (see FIGURE 1) of the housing is provided with a shaft opening through which a threaded adjustment shaft 12 (see FIGURE 2) of stainless steel or the like is inserted. Shaft 12 is supported on one end by the opening in the end wall 8 of the housing and at the other end 12a, the shaft is retained in a suitable support or opening, such as blind opening 15 shown in FIGURE 2. For operating the shaft externally of the housing 5, the shaft is provided with a slotted head 13, or other such shaped head, which may be easily operated by a screw driver or other appropriate tool.

As may be seen in FIGURE 5, there is provided, within the cavity 9, a base member or nonconductive support 10 which supports a resistance element 11 thereon. In this embodiment, as may best be seen in FIGURE 5, the base member is formed of a nonconductive ceramic material having deposited thereon a resistance film or track 11. The resistance track 11 may be formed of cermet material, conductive plastic, deposited carbon or other such suitable resistance material. Also mounted on the base member 10 is a suitable collector track 11a which usually runs parallel to and coextensive with the resistance track 11. The respective resistance track 11 and collector tracks 11a are electrically connected to suitable terminals, such as terminals 14 (see FIGURE 1) adapted to protrude from the housing for connecting the device into an electrical circuit.

As may best be seen in FIGURE 2, there is provided a contact carrier assembly which includes a contact carrier block 16 and an electrically conductive contact member 17 suitably attached thereto. The carrier block 16 is supported for movement back and forth within the cavity 9 of the housing and engages the threads 18 formed on the threaded shaft 12. The carrier block 16 is preferably molded of a plastic insulating material, such as molybdenum disulfide filled nylon and is preferably directly mounted on the shaft 12. If mounted on the shaft the block should include an aperture having threads formed therein to mate with the threads of the shaft. Or, in some instances the aperture may be made over size and the threads of the shaft may cut their own seat within the aperture as the block 16 is threaded onto the shaft. In the preferred embodiment of the invention, the block 16 is formed of a plastic material, such as the above mentioned molybdenum disulfide filled nylon, and the threads formed in the block within the aperture are sufliciently pliable to permit the shaft 12 to be turned with respect to the threads of the block if the block is restrained from movement. In this way, the fit between the threads of the block and the threads of the shaft forms a clutching arrangement so that, when the block 16 is moved to the end of its travel, such as shown in FIGURE 2, the shaft 12 may rotate with respect to the block. Other such clutching arrangemerits have been used in the past, such as threaded sleeve insert within the aperture of the block which rotates within the aperture when movement of the block is confined.

When, as shown in FIGURE 2, the block 16 reaches the end of its travel, means within the housing, such as the stop means or shoulder 19 formed on the end wall 26 of the housing, abuts against the block and prevents further movement thereof on rotation of the shart 12. Note, that the stop means does not necessarily have to extend from the end wall 26 and that the end wall itself might serve as the stop means. As mentioned above, the clutching arrangement between the shaft 12 and the block 16 permits the shaft 12 to rotate with respect to the block 16 without moving the block until the direction of the shaft rotation is reversed.

In order to provide an audible sound signifying that the block has reached its end position, a clicking mechanism is provided which moves with the block 16. In the embodiment disclosed in FIGURES 2-5, the clicking mechanism comprises a spring member 20, formed substantially into the shape of an M, with a slight bend 25 at its midsection and a pair of downwardly extending arms 21 and 22. The spring member is formed of a resilient type metallic material, such as a berylium-copper alloy or other suitable material. In this embodiment of the invention, the spring member 20 rides in a groove 23 formed in the top or upper side wall 24 of the housing above the block 16. The spring member 20 is locked in position by the slider block 16 and the ends 21 and 22 of the spring member extend downwardly along the side of the block but spaced therefrom. The ends of the arms 21 and 22 extend into the helical groove formed by the threads 18, as may best be seen in FIGURE 2.

On movement of the block 16, the spring member 20, which is associated with the block 16, moves back and forth within the cavity 9 and more specifically within the groove 23. When contact block 16 reaches its extreme end of travel on the resistance element so that it abuts the stop block 19, and the shaft 12 is further rotated, the downwardly extending arm 22 of the spring member 20 is depressed from position A to position B whereupon it rides over or is forced upwardly over the crest of the thread 18 on the shaft and snaps back to position A making a clicking sound.

When the rotation of the shaft 12 is reversed, the threads on the shaft engage the threads on the block 16 and the block begins to move in the opposite direction. Since the spring member 20 is no longer confined by the end wall of the housing and by the block 16, it also moves in a corresponding manner with the spring arms 21 and 22, or ends of the spring arms, riding in the helical groove of the shaft. When the block 16 is traversed to the other end of the housing and abuts against a stop means at this end of the housing, the end 21 of the spring member 20 is caused to ride over the threads 18 of the shaft and produces a clicking noise as it moves over the crest of each respective thread.

Note, in FIGURE 2, that the portion of the shaft adjacent the side wall 26 of the cavity is relieved of threads for a short distance into the cavity. By this arrangement, the end 21 does not engage threads when the block is moved to the end of its travel against stop 19. While this is the preferred embodiment, it is not absOlutely essential to eliminate the threads from the shaft in that portion thereof engaged by the end of the clicking spring arm proximate the end of the cavity. It is possible to employ threads on this portion of the shaft and to make both arms 21 and 22 of the spring snap over the crest of threads when movement of the block 16 is restrained.

Other means than that shown in FIGURES 2-5 may be employed for retaining the spring member in position with respect to the block 16. For example, such means are disclosed in the embodiment shown in FIGURES 6-8. In this embodiment, the spring member 30 comprises a U- shaped configuration with downwardly extending arms 31 and 32. As may be seen in FIGURES 6 and 7 the spring member is stamped or otherwise fabricated with a pair of punched indents or pointed tabs 33 which are bent over and forced into the sides of the block 16. Indents 33 not only support the spring member 30 on the block 16 but also serve to space the responsive arms 31 and 32 from the sides of the block 16. It is preferable that the tabs 33 be formed adjacent the connector section of the spring or adjacent the base of the arms 31 and 32 in order to permit sufficient movement of the arms within the helical groove formed by the shaft when the block 16 is restrained from movement. As in the previous embodiment, continued shaft rotation at either extreme end travel will operate the clutch mechanism of the block 16 and cause the engaged spring arms 31 and 32 to snap from one thread 18 to the next to product an audible clicking sound.

While in accordance with the patent statutes there has been described what at present is considered to be the preferred embodiment of the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, the aim of the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A variable resistance device comprising:

a housing enclosing a cavity, said housing having a shaft opening through a wall thereof;

a resistance element mounted in said cavity;

a threaded shaft mounted within said cavity substantially parallel to said resistance element and having an end thereof protruding through said shaft opening for rotating said shaft;

a contact carrier block in said cavity and having a portion thereof engaging the threaded section of said shaft for movement within said cavity on rotation of said shaft;

stop means on opposite ends of said cavity for restraining movement of said block beyond predetermined limit points during rotation of said shaft;

a clicking mechanism associated with said block and adapted to move therewith including a substantially U-shaped spring member having a pair of arms positioned on opposite sides of said block and extending downwardly adjacent the sides of said block with the ends thereof normally positioned in the groove of said threaded shaft, said U-shaped spring member being separate from said block and said distance between said arms of said member being sufiicient to space at least one arm thereof from the side of said block to permit axial movement of said arm with respect to said block when movement of said block is restrained by said stop means so that the end of said spring arm is moved substantially in the axial direction until it disengages from said thread and is caused to snap over the crest of said thread into the next groove of said threaded section of said shaft to produce a clicking noise.

2. A variable resistance device comprising:

a housin including side walls and end walls enclosing an elongated cavity, said housing having a shaft opening through an end wall and having stop means on opposite ends of said cavity;

a resistance element mounted in said cavity;

a contact carrier assembly including a nonconductive carrier block formed of a plastic material and an electrically conductive contact means extending from said carrier block and engaging said resistance ele ment, said contact carrier block and said contact belng mounted in said cavity above said resistance element and confined within said cavity for movement in a path parallel to said resistance element, said carrier block having a threaded aperture therethrough;

a rotatable shaft extending through said shaft opening in said wall of said housing into said cavity, said shaft havin a threaded section adapted to engage said threaded aperture through said contact carrier block and cause said carrier block to reciprocate in a path over said resistance element during rotation of said shaft, said threaded section of said shaft having a length less than the distance between said respective stop means on the opposite ends of said cavity;

longitudinal groove formed in a side wall of said housing within said cavity adjacent a surface of said contact carrier block;

clicking mechanism comprising a spring member formed substantially in a shape of an M, said spring member being separate from said block but adapted to move therewith, said central portion of said member being positioned within said longitudinal groove formed in said side wall of said housing with said arms of said spring member extending around the sides of said carrier block into engagement with the groove formed in said threaded section of said shaft, said spring member being confined within said longitudinal groove of said housing and adapted to move along said longitudinal groove as said carrier block moves, said respective arms of said spring member being spaced from the sides of said block so that when said block is restrained by said stop means at least one of said spring arms is moved in the axial direction until it disengages from said thread of said shaft and is caused by the resiliency of said spring to snap over the crest of said threads of said shaft to produce a clicking noise.

References Cited UNITED STATES PATENTS ROBERT K. SCHAEFER, Primary Examiner.

20 H. J. HOHAUSER, Assistant Examiner.

US. Cl. X.R. 

